In manufacturing semiconductor components, in particular in manufacturing cantilevered sensor structures by surface micromechanical technology, selective removal of a certain layer, a so-called sacrificial layer, selectively with respect to the functional layer, is an often necessary measure. Such a sacrificial layer may be removed, in principle, by dry chemical or wet chemical methods. Sacrificial layers are preferably removed with the aid of gaseous etching media, since when using etching gases, the risk of irreversible adhesion of sensor structure elements to the silicon substrate thereunder or of parts of the sensor structure elements to each other, the so-called sticking risk, is considerably reduced or eliminated.
In manufacturing micromechanical structures or components, silicon is mostly used as a functional layer due to its outstanding properties for these applications. Single-crystal silicon or polycrystalline silicon, in particular the so-called epi-polysilicon, i.e., epitaxially deposited polycrystalline silicon, is often used as a sensor functional layer from which the sensor structure elements are structured. In connection with silicon sensor structure elements, silicon-germanium (SiGe) is a particularly suitable sacrificial layer material.
An etching gas in non-plasma dry chemical etching processes may be chlorine trifluoride (ClF3). Chlorine trifluoride is normally stored in pressurized gas bottles which contain the substance in a liquefied form. Since liquid ClF3 is extremely reactive and, as a strong oxidizer, very hazardous, and since unintended release may cause severe damage, chlorine trifluoride is avoided by many users despite its advantageous properties.
German patent document DE 102 29 037 A1 discusses a method and a device using which ClF3 is produced with the aid of a high-density downstream plasma excitation prior to the actual etching process from relatively harmless gases such as chlorine or HCl on the one hand and sulfur hexafluoride, nitrogen trifluoride or fluorine on the other hand, and subsequently supplied to a process chamber in which etching is carried out.
The disadvantage of the known etching processes is that the achievable selectivity of etching silicon-germanium with respect to silicon limits the manufacture of complex structures and geometries by semiconductor technology using controlled removal of materials, in particular controlled removal of sacrificial layers, for example, in layer stacks, in the manufacturing processes of semiconductor components.